Concrete slab hoisting apparatus

ABSTRACT

A socket cavity formed in a concrete slab of the type poured horizontally and subsequently tilted up, which cavity affords engagement of hoisting equipment to the slab. The inner portion of the cavity is in the form of a frusto-conical wall surface communicating with the surface of the cavity through a cylindrical bore concentric with the frusto-conical surface. The cavity is formed by placing in the slab form an expendable flask-like hollow article formed of synthetic resin or the like which is left in the slab after erection thereof. Engaging apparatus cooperable with the cavity which has on the inner end thereof arms that are pivotally moveable between a retracted position and an extended position, the arms engaging the frustoconical wall of the cavity when in the extended position. The apparatus includes mechanism at the outer end thereof for effecting retraction or extension of the arms, the mechanism being remotely operable so as to afford disengagement of the hoisting mechanism from the slab from a remote location after erection of the slab.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to apparatus for engaging a concrete slab duringhoisting of the same.

2. Description of the Prior Art

U.S. Pat. Nos. 361,927; 560,329; 880,962 and 2,563,164 disclose"Lewises" which cooperate with a dovetail shaped slot in a block ofbuilding stone to afford a grip on the stone.

U.S. Pat. No. 3,652,118 discloses a lifting anchor for concrete slabswhich employs a wedge engageable with a socket cast in the concreteslab.

U.S. Pat. No. 3,590,538 discloses a threaded socket cast into a concreteslab which can be engaged by a threaded bolt.

U.S. Pat. Nos. 3,431,012; 3,596,971 and 3,705,469 disclose concrete slabengaging devices which are operated by rotation of a hoisting memberrelative to a socket formed in the slab.

Copending commonly assigned U.S. application Ser. No. 641,529 filed Dec.17, 1975 discloses a socket formed in a concrete slab and a mechanismfor effecting selective engagement in the socket for hoisting the slab.

SUMMARY OF THE INVENTION

According to the present invention there is formed in a concrete slab byan expendable low cost member a socket cavity having an inner end whichis of frusto-conical form and which communicates through a coaxialcylindrical portion to the surface of the slab. When concrete of whichthe slab is formed has set, a high strength socket for engagement by ahoisting mechanism is formed. The invention provides such engagementmechanism which can be quickly inserted into the socket to afford a gripon the slab to permit hoisting of the same for transportation anderection at the construction site.

An object of the invention is to provide a socket cavity of the typereferred to above which can be formed quickly and economically in aconcrete slab. This object is achieved by forming an expendable hollowmember having a shape corresponding to the socket, placing one or moreof the hollow members in the slab form prior to introduction of fluidconcrete thereinto and then pouring the concrete.

A feature and advantage afforded by the invention is that the hollowmember is concentric with a central axis so that the loading from thefluid concrete thereon is sufficiently uniform that relatively thinlightweight and inexpensive material, such as synthetic resin material,can be employed.

Another object is to provide a reuseable socket engaging mechanismcooperable with the socket formed as described above which can bequickly and conveniently engaged without attention to rotativeorientation within the socket. This object is achieved because of thesymmetry of the above mentioned frusto-conical portion and the symmetryof the engaging mechanism. Achievement of this object is facilitatedbecause the engaging mechanism employs two or more uniformly spacedapart arms and a simple mechanism for pivoting the arms from a retractedposition to a protruding position at which they engage the inner wall ofthe frusto-conical portion of the socket formed as described above.

A further object is to provide an engaging mechanism which can bedisengaged from a remote site. The importance of achieving this objectcan be appreciated by considering that when a slab reaches its finalposition at a construction site, the engaging members are typicallylocated well above ground level so that the ability to free the engagingmechanisms from a remote location eliminates the necessity for employinga ladder or the like to gain access to the engaging mechanisms. Thisobject is achieved in the present invention by providing an axiallymoving operating rod which cooperates with the above mentioned arms sothat upon axial movement of the rod the arms are retracted. On the outerend of the structure is a pivot lever which can be pivoted by force on alanyard secured thereto so as to effect disengagement of the arms andconsequent ready removal of the engaging mechanism from the slab socket.

The foregoing together with other objects, features and advantages willbe more apparent after referring to the following specification and theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a slab socket and engagingmechanism according to the invention.

FIG. 2 is a cross-sectional elevation view of a concrete slab having asocket formed therein in accordance with the invention.

FIG. 3 is a fragmentary perspective view of the socket engaging means ofthe invention engaged in the socket.

FIG. 4 is a cross-sectional view in elevation taken along an arcuateplane designated by line 4--4 of FIG. 1 and showing the engagingmechanism in place in the socket cavity in a disengaged position.

FIG. 5 is a fragmentary view similar to FIG. 4 showing the engagementmechanism in an engaged position.

FIG. 6 is a cross-sectional view taken along a plane designated by line6--6 of FIG. 5.

FIG. 7 is a cross-sectional view taken along a plane designated by line7--7 of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring more particularly to the drawings reference numeral 12indicates a concrete slab in which is formed in accordance with theinvention a socket cavity indicated generally at 14, the interior ofwhich cavity is accessible from a surface S of slab 12. A socketengagement mechanism 16 is arranged for selective engagement anddisengagement with the walls of socket cavity 14 and has facilities forengagement by a hoisting line during transportation and erection of theslab.

For forming socket cavity 14, the invention provides a hollow flask 18which is preferably constructed of low cost material such as moldedsynthetic resin. The flask includes a cylindric neck portion 20 which isintegral and concentric with a frusto-conical portion 22. Spanning theend of frusto-conical portion 22 remote from cylindrical portion 20 is acircular end wall 24, also preferably integral with the frusto-conicalportion 22. End wall 24 defines the inner end of the hollow cavitydefined by flask 18. The conical angle of frusto-conical portion 22 withrespect to the cylindric axis of cylindric portion 20 is, in theembodiment shown in FIG. 2, approximately 13°. This angle is largeenough to afford firm engagement with the cavity (by mechanism describedhereinbelow) but small enough to avoid imposing substantial shearstresses on the concrete in slab 12 above the conical wall portion. Thepreferred range of conical angles is 13° plus or minus 3°, that is, fromabout 10° to about 16°.

During formation of slab S, it is essential to exclude fluid concretefrom entry into the cavity defined by flask 18. For closing the end ofthe flask opposite end wall 24 there is a plug 26. As described in theabove cited copending application, the plug is formed of imperviousplastic material and has a cylindric wall portion 28 which is sized fora telecoping substantially fluid tight fit within cylindric wall portion20 of the flask. Cylindric wall portion 28 is integral with and dependsfrom an impervious circular disc 30 from the upper periphery of whichextend a plurality of fingers 32. The fingers are of sufficiently smallsize that they are deformable so that in pouring the concrete up to alevel coincident with surface S, the fingers deform or yield whenfinishing tools are moved over the surface. Moreover, the fingers,because they are spaced apart from one another, form a circularperforated line between concrete interior of the fingers and theconcrete exterior thereof, wherefore the plug can be located and removedwhen the concrete has hardened.

A slab 12 with one or more cavities 14 formed therein can be quicklyengaged for hoisting by socket engagement mechanism 16. The socketengagement mechanism 16 includes a main shaft 34 having a diameter lessthan the diameter of cylindric wall portion 20 of flask 18 and thecavity formed by the flask. Rigid with the inner end of shaft 34 iscylindric enlargement 36 which has a diameter substantially equal to theinner diameter of cylindric portion 20 of the socket cavity so that theenlargement and the main shaft are supported substantiallyconcentrically of the cavity. Enlargement 36 is formed with a pluralityof uniformly spaced apart radially extending slots 38 in each of whichan arm 40 is pinned by a pin 42 to afford pivotal movement of the armbetween a retracted position (FIG. 4) and extended position (FIG. 5).Because arms 40 are identical, the description of one should beconsidered the description of all.

As can be seen most clearly in FIG. 6, the inner radial extremities ofarms 40 are foreshortened so as to define a central space to accommodatean operating rod 44. The lower free ends of arms 40 extend belowenlargement 36 and the arms each define distally of pin 42 a sectorshaped portion or sector 46. Each sector 46 has an exterior arcuatesurface 46S which, as can be seen in FIGS. 5 and 7, conforms to thecurvature of the inner surface of frusto-conical surface portion 22 ofcavity 14. Each sector 46 also has an inward facing curvilinear cammingsurface 46C which cooperates with a distal cylindric portion 48C ofconical cam 48 that is rigid and preferably integral with rod 44. At thedistal extremities of respective curvilinear camming surfaces 46D thereare concave arcuate surface regions 46R, each of which is configured toreside coaxially of cylindric portion 48C of conical cam 48. Eacharcuate surface region 46R merges smoothly into curvilinear cammingsurface 46C so that outward axial movement of the conical cam moves arms40 to the extended position. The radius of curvature of arcuate surfacesregion 46R is equal to that of cylindric portion 48C of conical cam 48so that when arms 40 are moved to the extended position there is africtional, surface-to-surface contact between the concave arcuateregion 46R and cylindric portion 48C. The inner surface of each sector46 is excised or relieved at 50 to define a camming surface 50C having aconfiguration corresponding to conical cam 48 so that the arms are movedto a retracted position shown in FIG. 4 when rod 44 and cam 48 are movedinward.

Shaft 34 is externally threaded for threaded enagement with aninternally threaded collar 52 so that the collar can be axiallypositioned along shaft 34 by rotation of the collar with respect to theshaft. Integral with the collar is a flange 54, the lower surface 54S ofwhich is normal to the axis of shaft 34 so that surface 54S can bearagainst slab surface S to position the inner end of engaging mechanism16 in an appropriate location for engagement with frusto-conical wallsurface 22. Projecting perpendicularly of flange surface 54S is a collarextension 56 which has an outer diameter corresponding to the innerdiameter of cylindric portion 20 of the cavity so that in the positionshown in FIG. 4, rod 34 will be supported substantially concentric withthe axis of cylindric portion 20.

Rigid with the outer or upper end of rod 34 is a U-shaped stirrup 58which supports an operating lever 60 for pivotal movement about the axisof aligned pins 62. The inner end of lever 60 is bifurcated, and betweenthe furcations is supported a block 64 by means of a pin 66 whichextends through the block and the furcations.

Because the axis of pins 62 is spaced from the axis of pin 66, pivotalmovement of lever 60 about the axis of pin 62 effects vertical movementof block 64. Block 64 defines a horizontally oriented slot 68 which isintersected by a vertically extending opening 70, the opening 70 havingan extent larger then the diameter of operating rod 44 which extendsthrough the opening. The upper extremity of operating rod 44 has anenlarged head 72 which resides within slot 68. Head 72 is of lesservertical extent than slot 68 so as to avoid interference with lateralmovement of block 64 in response to pivotal movement of lever 60. Foraffording a grip on engagement mechanism 16 during hoisting of aconcrete slab with which the mechanism is engaged, there arediametrically extending stub shafts 74 rigid with collar 52. Pivotallysecured on the outer ends of the stub shafts is a U-shaped bail 76 whichhas a vertical extent sufficient to clear lever 60.

In operation, one or more flasks 18, each supplied with plug 26, aredisposed in a concrete form which is typically oriented in a flat orhorizontal position. The flasks are positioned so that the upper surfaceof the finished slab to be poured into the form will reside at aposition above the mouth of flask 18 by a distance approximately equalto 1/3 of the length of fingers 32. Thereafter, the concrete is placedand finished, the deformability of the fingers avoiding interferenceduring the finishing process. When the concrete has cured or hardened,plugs 26 are removed, an operation which can be performed easily becauseof the perforations formed around the concrete overlying the socketopening.

When it is desired to hoist the slab containing one or more cavities 14formed as described above, a corresponding number of socket engagingmechanisms 16 are employed, one in association with the cavity. It ispreferred that collar 52 and integral plate 54 are rotated so as to movethe collar and plate upward on shaft 34. Next lever 60 is moved to theposition shown in solid lines in FIG. 4 so as to retract arms 40 and topermit entry of the mechanism into the cavity. Cooperation betweenconical cam 48 and camming surfaces 50C on the inner surfaces of arms 40retracts the arms when rod 44 is moved upward. When socket engagementmechanism 15 is inserted into the cavity to an extent that arms 40 reachthe bottom of the cavity and contact circular end wall 24, lever 60 ispivoted in a counterclockwise direction, as viewed in FIG. 4, so as tomove rod 44 and cam 48 downward thereby to move arms 40 to theprojecting position as seen in FIG. 5. Next collar 52 and integral plate54 are threaded downward along shaft 34 until surface 54S contacts slabsurface S. Further turning of the collar and plate move shaft 34 andprojecting arms 40 upward into firm engagement with frusto-conical wallportion 22 within the cavity. The socket engagement mechanism 16 is thusfirmly engaged and hoisting can proceed by engaging a hoisting line withbail 76. As can be seen most clearly in FIG. 7, exterior surfaces 46S ofsectors 46 each has a circumferential extent of about 60° so as toafford a large area of contact between the socket engagement mechanismand the walls of the socket cavity.

It will be noted in FIG. 5 that there is a clearance space between thebottom of the cavity defined by circular end plate 24 and the axialextremity of sectors 46 of arms 40. This clearance space has thefunction of permitting extension of arms 42 into engagement with thefrusto-conical walls of the cavity nothwithstanding the presence ofparticles of concrete within the cavity, such as might enter the cavityduring removal of plug 22. Also assuring firm engagement of arms 40 withthe frusto-conical wall of the cavity in the presence of concreteparticles in the cavity is the fact that rod 44 moves outward in movingthe arms to the extended position. Accordingly, the likelihood that thepresence of small particles of concrete or like deleterious substanceswithin cavity 14 will interfere with firm engagement with the walls ofthe cavity is extremely small.

The presence of cylindric surface 48C on cam 48 together with thearcuate configuration of surfaces 46C on sectors 46 assures secureengagement between socket engaging mechanism 16 and the walls of cavity14, particularly when the parts are subjected to loading during hoistingof a slab. The foregoing can be appreciated most readily by reference toFIGS. 5 and 7. In such figures it will be noted that surfaces 46C have asubstantial surface area of contact with cylindric surface 48C on cam48. Because of the substantial area of surface contact and because ofthe substantial normal force arising from the weight of the slab, thefrictional force between surfaces 46C and 48C is sufficiently great toreduce if not virtually eliminate the likelihood of disengagement frominadvertent axial movement of rod 44. When the normal force is reducedby slacking off on the hoisting line secured to bail 76, however,retraction of arms 40 and disengagement of the mechanism from the slabcavity can be readily effected by restoration of lever 60 to the solidline position shown in FIG. 4. The foregoing movement of lever 60 can beachieved from a remote location, i.e. from ground level, by applicationof tension to a lanyard 78 (see FIG. 1) that is attached to the free ordistal end of lever 60.

Thus it will be seen that the present invention provides an inexpensiveand efficient mechanism for hoisting concrete slabs duringtransportation and erection thereof. The low expense follows from thefact the flask 18, an expendable part, is formed of molded syntheticresin of light weight and low cost. Because the flask is subjected toloading only until the concrete hardens and such loading is confinedsubstantially to uniform compressive loading, the flask can be made ofrelatively light weight low strength material. Moreover, thefrusto-conical shape, in addition to providing for firm engagement withsocket engaging mechanism 16, firmly retains grout within the socketcavity which grout is typically placed therein after the slab is erectedto its final position.

The socket engaging mechanism in cooperating with the cavity permitsquick adjustment to accommodate for varying depths of socket cavitiesand can reside at any rotative position throughout a full 360° arc.Moreover, extension of arms 40 can be achieved when the arms are in anunloaded condition because of the clearance space between the axialextremity of the arms and the lower wall of the cavity; the amount offorce necessary to move lever 60 to the engaged position is thusminimized. Finally, the fact that the lever traverses an arc of lessthan about 90° between the engaged and disengaged position permits thesocket engaging mechanism to be disengaged from the remote locationthereby eliminating the time and expense of obtaining a ladder or thelike to remove the mechanism once the slab is hoisted into place.

Although one embodiment of the invention has been shown and described itwill be obvious that other adaptations and modifications can be madewithout departing from the true scope and spirit of the invention.

What is claimed is:
 1. Apparatus for engaging a concrete slab to hoistthe same, said slab having a generally planar surface, said apparatuscomprising in combination: a socket cavity in said slab, said cavitybeing elongated along an axis substantially normal to said surface andsymmetrical about said axis, said cavity having a cylindric portioncommunicating with said surface and a frusto-conical portion below saidsurface accessible through said cylindric portion and coaxial therewith,said frusto-conical portion defining a wall that converges in adirection toward said surface; a shaft having a diameter less than saidcylindric portion and a length greater than the depth of said cavity,said shaft having an inner end and an outer end, a cylindricalenlargement on said inner end defining a bearing surface ofsubstantially the same diameter as said cylindric portion and beingcoaxial with said shaft; at least three arms secured to said inner endat equal angularly spaced positions therearound for pivotal movementbetween a retracted position to afford insertion and removal of saidshaft relative said cavity and an extended position for engaging saidfrusto-conical wall; and means accessible from the outer end of saidshaft for controllably moving said arms between a retracted position andan extended position.
 2. Apparatus according to claim 1 wherein saidcavity defining means comprises an impervious synthetic plastic hollowbody having an interior shape corresponding to said cavity, said bodybeing of generally uniform thickness and having an exterior surface inintimate contact with the concrete of the slab.
 3. Apparatus accordingto claim 1 wherein the conical angle of said frusto-conical portionrelative the axis of said cylindric portion is in the range of about10°-16°.
 4. Apparatus for engaging a concrete slab having asubstantially planar surface and a symmetrical socket cavity having acylindric portion normal to and opening onto said surface, said cavityhaving a frusto-conical portion communicating with and coaxial with saidcylindric portion, said apparatus comprising a shaft having a diameterless than said cylindric portion and a length greater than the depth ofsaid cavity, said shaft having an inner end and an outer end, acylindrical enlargement on said inner end defining a bearing surface ofsubstantially the same diameter as said cylindric portion and beingcoaxial with said shaft, means including at least three arms secured tosaid inner end at equal angularly spaced positions therearound forpivotal movement between a retracted position to afford insertion andremoval of said shaft relative said cavity and an extended position forengaging said frusto-conical wall, and means accessible from the outerend of said shaft for controllably moving said arms between a retractedposition and an extended position.
 5. Apparatus according to claim 4wherein said shaft has an externally threaded portion remote from saidenlargement, a collar having interal threads engagable with the threadedportion of said shaft so as to position said collar along said shaft inresponse to rotation thereof and a flange rigid with said collar andhaving a surface normal to said shaft for bearing on said slab surface.6. Apparatus according to claim 4 wherein said arms have arcuateexternal surfaces having the same curvature as said frusto-conicalportion so as to effect engagement of said frusto-conical portion over asubstantial surface area.
 7. Apparatus according to claim 4 wherein saidarm moving means comprises a rod, a bore centrally of said shaft forsupporting said rod for axial movement within said bore, a cam rigidwith the end of said rod adjacent said arms, said cam defining acylindric surface portion concentric with said rod, said arms havinginward facing curvilinear camming surfaces for cooperating with saidcylindric surface portion of said cam so that outward axial movement ofsaid cylindric surface portion of said cam along said curvilinearcamming surfaces moves said arms radially outward to the extendedposition.
 8. Apparatus according to claim 7 wherein said inward facingcurvilinear surfaces define at the distal extremity of said armsconcavefarcuate surfaces having a curvature corresponding to saidcylindric surface portion of said cam, said arcuate surfaces having anarea sufficient to frictionally engage said cylindric surface portion ofsaid cam to inhibit axial movement of said rod when said cavity wallengaging means is engaged in said cavity and is in a loaded condition.9. Apparatus according to claim 7 wherein said cam includes afrusto-conical surface portion axially inward of said cylindric surfaceportion and wherein each said arm defines an excision axially inward ofsaid curvilinear camming surface, said excisions defining inward facingfrusto-conical surface portions corresponding to said frusto-conical camsurface portion so that inward axial movement of said cam cooperateswith the frusto-conical camming surfaces on said arms to radially movesaid arms to the retracted position.
 10. Apparatus according to claim 6wherein said arm moving means includes a lever, means for mounting saidlever to the outer end of said shaft for pivotal movement about an axisnormal to said shaft, and means for linking said rod to said lever sothat said rod moves axially in response to pivotal movement of saidlever. .Iadd.
 11. Apparatus for the releasable connection to a tubularmember embedded in an object, the member defining an opening in theobject and including an inwardly facing shoulder disposed interiorly ofthe opening, the apparatus comprising: plate means adapted to be placedacross the opening and including an aperture for alignment with theopening; an elongate housing extending through the aperture and havingan axial bore, the inner end of the housing being adapted forpositioning in said opening, and including a laterally extending cutout,a locking lug carried by the housing for lateral movement within thecutout from a first position in which the lug is out of engagement withthe shoulder to a second position in which a portion of the lugprotrudes laterally from the housing into engagement with the shoulder;and actuating means slidably disposed in the bore for moving the lugbetween the first and second positions responsive to movement of theactuating means longitudinally in the bore between corresponding firstand second positions; the actuating means including means for positivelyand mechanically locking the lug in its second position when theactuating means is in its second position. .Iaddend.